ARM: EXYNOS: register power domain driver from core_initcall

SYSMMU devices are registered very early in arch_initcall, so ensure
that they can get access to power domains by registering power domain
driver from earlier initcall. This change requires dropping usage of
the platform device associated with each power domain and replacing
clock calls with respective of_clk_* equivalents.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>